The proposed work studies intravenous self-administration of amphetamine and cocaine in rhesus monkeys. The effects of anti-dopaminergic drugs such as chlorpromazine and haloperidol have been investigated on behavior maintained by the stimulants and also on behavior maintained by food. Stimulant reinforced behavior is specifically sensitive to the effects of the neuroleptics, being increased or decreased at doses that have very little effect on food-reinforced behavior. The effect of chlorpromazine on amphetamine self-administration appears to involve antagonism of both the direct effect of the stimulant and antagonism of the reinforcing property as well. We now intend to investigate the effect of anti-cholinergic drugs on behavior maintained by central stimulants and by food, to determine whether there is a specific drug-drug interaction with these compounds as well.